This application is based on application No. 98-50402 filed in the Korean Industrial Property Office on Nov. 24, 1998, the content of which is incorporate herein by reference.
(a) Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube having a substantially rectangular cone portion in which an inner graphite layer can be formed to an optimum thickness on the rectangular cone portion such that high voltages are more uniformly transmitted therethrough.
(b) Description of the Related Art
A cathode ray tube(CRT) is a device for displaying images on a screen by emitting electron beams from an electron gun assembly and landing the electron beams onto a phosphor screen. Conventional CRTs include a vacuum envelop having a panel on which the phosphor screen is formed, a neck in which the electron gun assembly is arranged, and a funnel formed between the panel and the neck.
Immediately after the electron beams are emitted, they are horizontally and vertically deflected by magnetic fields generated by a deflection yoke. Thus, the electron beams strike all pixels on the phosphor screen. The deflection yoke is mounted on the exterior of the funnel, i.e., on a cone portion of the funnel. The cone portion is formed contiguous to the neck. A cross section of the cone portion typically reveals a circular form, and a cross section of the deflection yoke reveals an inner circumference that is circular.
In such a CRT, the deflection efficiency of the deflection yoke is low since there is a considerable amount of space between deflection coils of the deflection yoke and the electron beams. To improve the deflection efficiency, power applied to the deflection yoke is increased. However, this increases the overall power consumption of the CRT and induces leakage of the magnetic fields.
To solve these problems, a cone portion having a cross section that gradually changes from a circular form of the neck to a rectangular form of the panel has been developed. Because a shape at which the electron beams passing inside the cone portion is distributed substantially rectangular to correspond to the rectangular image produced on the panel, the cone portion is made into as close a shape to match the rectangular distribution shape of the electron beams as possible. Accordingly, an inner circumference of the deflection yoke mounted on the cone portion is also rectangular in shape.
Such a rectangular cone portion has various advantages. First, the electron beams can be prevented from striking the inner surface of the funnel since the rectangular shape provides space in the four diagonal portions on which the electron beams are likely to strike. Second, the deflection efficiency can be increased by enabling the electron beams to come close to the deflection coils in the horizontal and vertical portions of the cone portion. Third, power consumption of the deflection yoke and magnetic field leakage generated by the deflection yoke can be reduced.
However, the rectangular cone portion is not rotationally symmetical, and the four comers thereof are formed having curvatures rather than the horizontal and vertical portions. As a result, when the inner graphite layer is applied on the inner surface of the funnel, it is not as uniformly applied on inside comers as it is on inside horizontal and vertical walls of the cone portion.
The inner graphite layer is a conductive layer which is disposed on the inner surface of the funnel at a predetermined thickness, and acts to transmit a voltage applied through an anode button to an accelerating electrode of the electron gun assembly and the panel. Thus, the electron beams are focused by a difference in potential between the voltages applied to the accelerating electrode and a focusing electrode of the electron gun, after which the electron beams are accelerated onto the phosphor screen by the high voltage on the panel.
Hence, it is important that the inner graphite layer uniformly transmits the high voltage so that the electron beams are exactly focused and accelerated. Accordingly, the inner graphite layer must have a constant resistance. Since the resistance of the inner graphite layer is directly related to its thickness (i.e., greater thickness results in smaller resistance), it is essential that the inner graphite layer be evenly applied on the inner surface of the funnel.
However, because of the shape of the rectangular cone portion, the inner graphite layer can not be as evenly applied on the inside comers as on the inside horizontal and vertical walls of the cone portions. Consequently, a constant resistance over the entire inner graphite layer is not realized, thereby reducing the overall performance of the CRT.
It is an object of the present invention to provide a cathode ray tube having a rectangular cone portion in which an inner graphite layer is formed to an optimum thickness.
It is another object of the present invention to provide a cathode ray tube capable of uniformly transmitting a high voltage to an accelerating electrode of a electron gun assembly and a panel.
In order to achieve these objects, the CRT includes a rectangular panel, a cylindrical neck, a funnel between the panel and the neck having a rectangular cone portion contiguous to the neck, an anode button to supply a high voltage in the funnel, and an inner graphite layer disposed on an inner surface of the funnel to form a path for the transmission of the high voltage. The inner graphite layer satisfies at least one of the following conditions:
0.9xe2x89xa6Td/Thxe2x89xa61.36
0.9xe2x89xa6Td/Tvxe2x89xa61.36
where Td is an approximate thickness of the inner graphite layer disposed on each side corner of the cone portion, Th is an approximate thickness of the inner graphite layer disposed on inside horizontal walls of the cone portion, and Tv is a thickness of the inner graphite layer disposed on inside vertical walls of the cone portion.
When the inner graphite layer satisfies the above conditions, it can uniformly transmit the high voltage to the accelerating electrode of the electron gun assembly and the panel.
The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims as well as the appended drawings. It is also to be understood that both the foregoing general description and the following detailed description are not intended to limit the scope of this invention, many variations of which will be apparent to those with ordinary skill in the art. The disclosure of the specific embodiments are intended to provide further explanation of the invention as claimed.